// ClickPoint.js
// Vertex shader program
var VSHADER_SOURCE =
        'attribute vec4 a_Position;\n' +
        'void main() {\n' +
        ' gl_Position = a_Position;\n' +
        ' gl_PointSize = 10.0;\n' +
        '}\n';

// Fragment shader program
var FSHADER_SOURCE =
        'void main() {\n' +
        ' gl_FragColor = vec4(1.0, 0.0, 0.0, 1.0);\n' + // Set the color
        '}\n';

function main() {
        // Retrieve <canvas> element
        var canvas = document.getElementById('webgl');

        // Get the rendering context for WebGL
        var gl = getWebGLContext(canvas);
        if (!gl) {
                console.log('Failed to get the rendering context for WebGL');
                return;
        }
        // Initialize shaders
        if (!initShaders(gl, VSHADER_SOURCE, FSHADER_SOURCE)) {
                console.log('Failed to initialize shaders.');
                return;
        }

        // Get the storage location of attribute variable
        var a_Position = gl.getAttribLocation(gl.program, 'a_Position');
        if (a_Position < 0) {
                console.log('Failed to get the storage location of a_Position');
                return;
        }

        // Register function (event handler) to be called on a mouse press
        canvas.onmousedown = function(ev) { click(ev, gl, canvas, a_Position); };

        // Pass vertex position to attribute variable
        gl.vertexAttrib3f(a_Position, 0.0, 0.5, 0.0);


        // Set the color for clearing <canvas>
        gl.clearColor(0.0, 0.0, 0.0, 1.0);

        // Clear <canvas>
        gl.clear(gl.COLOR_BUFFER_BIT);

        // Draw a point
        gl.drawArrays(gl.POINTS, 0, 1);
}

var g_points = []; // The array for a mouse press

function click(ev, gl, canvas, a_Position) {
        var x = ev.clientX; // x coordinate of a mouse pointer
        var y = ev.clientY; // y coordinate of a mouse pointer
        var rect = ev.target.getBoundingClientRect();

        x = ((x - rect.left) - canvas.height/2)/(canvas.height/2);
        y = (canvas.width/2 - (y - rect.top))/(canvas.width/2);
        // Store the coordinates to g_points array
        //g_points.push(x); g_points.push(y);
        g_points.push([x, y]);

        // Clear <canvas>
        gl.clear(gl.COLOR_BUFFER_BIT);

        var len = g_points.length;
        for(var i = 0; i < len; i++){//i+=2) {
                // Pass the position of a point to a_Position variable
                //gl.vertexAttrib3f(a_Position, g_points[i], g_points[i+1], 0.0);
                var xy = g_points[i];
                gl.vertexAttrib3f(a_Position, xy[0], xy[1], 0.0);

                // Draw a point
                gl.drawArrays(gl.POINTS, 0, 1);
        }
}